1. Field of the Invention
The present invention relates to chemical disinfection and sanitizing and, more particularly, to an improved biocidal aldehyde composition particularly suited for secondary oil and gas recovery.
2. Description of the Background
The purpose of disinfection is to reduce microbial contamination to an innocuous level. There is a widespread need for effective antimicrobials across diverse industries, including for oil and gas recovery (for treatment, penetration and removal of biofilm). Without a biocide, microorganism growth leads to biofilm formation, which contributes to corrosion, contamination of oil and gas, and degradation of drilling muds and fracturing. There are a few existing commercial biocides that purport to solve the need. For example, Dow® sells a line of AQUCAR™ water treatment microbiocides which include various proportions of glutaraldehyde alone or in combination with other biocides such as acetone or ammonium chloride. Glutaraldehyde is an important high level disinfectant/sterilant also used in other industries such as health care. It requires time and temperature control (residence time of 45-90 minutes for disinfection, and controlled temperature of from 20 C to 25-30 C). Glutaraldehyde requires activation and dating to make it useful. Thus, proper usage entails a three step procedure and meticulous record-keeping regarding date of activation.
A different aldehyde, ortho-phthalaldehyde (OPA), has now come into use in the health care industry. Johnson and Johnson developed an original formulation in the late 1980s described in U.S. Pat. No. 4,851,449 and in subsequent continuation in part application(s). This OPA has been approved by the FDA as a high level disinfectant with a twelve minute disinfection time at 20-22 degrees C. Its sterilization time is listed between 24-32 hours. OPA interacts with amino acids and proteins of microorganisms. OPA is lipophilic, which improves its uptake in the cell walls. Thus, OPA has been shown to be another effective disinfectant/sterilant. The J&J OPA concentration is 0.55% by weight at a pH 3-9. It has been shown to be effective in a purely aqueous immersion solution. Metrex Research Corp. continues to sell a modified formulation referred to as OPA+, with an increased OPA concentration of 0.6% (0.05% more OPA), plus buffers, a corrosion inhibitor, and a chelating agent. In essence the formula is the same as the J&J product, with no faster kill time, but claims of 60% more treatment. However, if one looks at the mechanism by which OPA works it becomes biologically clear where the weaknesses lie. OPA is an aromatic dialdehyde. The severe test for cidal effectiveness are gram negative bacteria, mycobacteria and spore-coated organisms. OPA is not completely effective in clinical use at its concentration of 0.5% and pH 6.5. Failures occur and have been reported in literature surveys. The benzene ring of OPA is a planar, rigid structure. Therefore, OPA has no flexibility as a result of steric hindrance. In addition, OPA only reacts with primary amines. OPA is bactericidal at low concentrations to staphylococci and gram negative bacteria. The poor sporicidal activity is due to low concentration and low pH. It has been noted that if the temperature is raised from the normal 20 degrees C. to 30 degrees it improves. However, this is impractical. Regarding mycobacteria, a similar problem is present. The lipophilic aromatic component of OPA does not reliably penetrate the lipid-rich cell wall of mycobacteria and gram negative bacteria. Indeed, subsequent studies show that OPA exhibits selective bactericidal activity, good against Pseudomonas aeruginosa, limited activity against mycobacterial strains. See, Shackelford et al., Use of a New Alginate Film Test To Study The Bactericidal Efficacy Of The High-Level Disinfectant Ortho-Phthalaldehyde, Journal of Antimicrobial Chemotherapy, 57(2):335-338 (2006). Despite the lingering issues, OPA has been suggested for use as a biocide in oil and gas recovery applications. See, U.S. Pat. No. 5,128,051 to Theis et al. issued Jul. 7, 1992 which discloses providing ortho-phthalaldehyde to aqueous systems susceptible to biofouling, including secondary oil recovery processes.
Presently, there is no single universally effective biocide due to variable physical, chemical and biological parameters. A biocide must have interactions of a variegated nature in order to have a chance of reasonable effectiveness. What is needed is a simple and improved one-step formulation.
In copending U.S. patent application Ser. No. 12/584,650 filed Sep. 9, 2009 the present inventor suggests a synergistic combination of quaternary ammonium cations with an aldehyde selected from the group consisting of glutaraldehyde and orthophthalaldehyde, isopropyl alcohol, chlorine dioxide (ClO2), a proppant comprising a cellulosic compound selected from the group consisting of methylcellulose, ethylcellulose and hydroxymethylcellulose, a pluronic block copolymer, a flocculating agent, and water. The present inventor has established that the goal can be accomplished more effectively with combinations of tributyl tetradecyl phosphonium chloride (TTPC) (or, alternatively, tetrakis (hydroxymethyl) phosphonium sulfate (THPS)), with the following biocides: glutarladehyde, orthophthalaldehyde and/or isopropyl alcohol.
Thus, the present application discloses an improvement to the preceding formulation in which a quaternary phosphonium salt, preferably tributyl tetradecyl phosphonium chloride (TTPC), is substituted for the dual chain quaternary ammonium to achieve markedly improved results. Alternatively, Tetrakis (hydroxymethyl) phosphonium sulfate (THPS) may be used in lieu of TTPC. The following discussion is explanatory and evidenced based using either glutaraldehyde or OPA for more effective disinfection/sterilization in industrial/commercial uses such as oil and gas recovery.
TTPC has improved thermal and chemical stability based upon its unique miscibility and solvating properties. TTPC is less dense than water and is anion dependent, which makes it sensitive to various solutes and thereby a better component carrier for the glutaraldehyde, OPA, IPA, ClO2. It also enhances catalysis. TTPC is a phosphonium salt with the phosphonium ion (PH4+) replacing the amine of the dual chain quat formulation. The quat to be replaced had a tendency to foam especially above pH8. The mechanism of kill is cationic whereby an electrostatic bond is formed with the cell wall affecting permeability and denaturing proteins. The effective pH is 6-8.5 and is only bacteriostatic.
TTPC is a broad spectrum biocide of the alkyl phosphonium group. TTPC is cationic also but with low foaming tendency, a high level of hydrolytic stability, and it functions over a much broader pH range from 2-11. TTPC damages cell walls, as explained further, and affects cell enzyme process. TTPC is not affected by brine as is the dual chain quat formulation making it superior for oil field usage. TTPC kills at much lower concentrations than the dual chain quat formulation and is faster acting. TTPC aids in biofilm penetration and delays biofilm regrowth, which is extremely meaningful for oil/gas usage. TTPC is a neoteric solvent/biocide that has been developed with remarkable individual properties. It is an ionic liquid that has microbicidal qualities, solvent qualities, and detergent qualities.